Pisen Electronics via Amazon offers the Pisen 20,000mAh Portable Charger Power Bank in Black or White for $29.99. Coupon code "RT9EH27U" cuts it to $19.79. With free shipping, that's tied with last week's mention, $10 off, and the lowest price we could find. It features one micro USB cable, 5V 2A input for quick charging, and a smart digital display LCD screen. Deal ends December 31.